The invention relates to the use of free-radically polymerized, UV-crosslinkable addition polymers which consist to the extent of at least 50% by weight of C2 to C18 alkyl(meth)acrylates as adhesives for the bonding of carriers coated with the polymer on substrates, wherein from 0.1 to 30% by weight of the monomers of which said polymer is composed are monomers A without carboxylic acid or carboxylic anhydride groups and with a water solubility of more than 5 g of monomers per liter of water and said substrates are moist substrates, especially refrigerated substrates.
UV-crosslinkable polymers and their use as adhesivesxe2x80x94as hot-melt pressure-sensitive adhesives, for examplexe2x80x94are known from DE-A-2 411 169, EP-A-246 848, DE-A-4 037 079 or DE-A-3 844 444, for example.
These adhesives have not been used to date for moist substrates, especially refrigerated substrates.
For producing labels for refrigerated product it is normal to use block polymers of the styrene-isoprene-styrene or styrene-butadiene-styrene type. A general disadvantage of these block copolymers lies in their softness, which leads to difficulties in the course of processing and use.
There is a desire for alternative polymers as adhesives for moist, refrigerated substrates.
It is an object of the present invention to provide alternative polymers for such a use.
We have found that this object is achieved by the use defined at the outset.
For crosslinking with UV light, the addition polymer may contain a photoinitiator. The photoinitiator may be attached to the polymer but may also be unattached and merely mixed with the polymer.
Customary photoinitiators that can be added to the polymer are, for example, acetophenone, benzoin ethers, benzil dialkyl ketals, or derivatives thereof.
The amount of photoinitiator mixed in is preferably from 0.05 to 10 parts by weight, with particular preference from 0.1 to 2 parts by weight, per 100 parts by weight of polymer.
Through irradiation with high-energy light, especially UV light, the photoinitiator or photoinitiator group brings about a crosslinking of the polymer, preferably by means of a chemical grafting reaction of the photoinitiator group with a spatially adjacent polymer chain. Crosslinking can be effected in particular by inserting a carbonyl group of the photoinitiator into an adjacent Cxe2x80x94H bond to form a xe2x80x94Cxe2x80x94Cxe2x80x94Oxe2x80x94H grouping.
The wavelength range within which the photoinitiator group can be activated, i.e., that in which the principal absorption band of the photoinitiator group lies, is preferably from 200 to 450 nm, with particular preference from 250 to 350 nm, with very particular preference from 250 to 280 nm.
Preferably, the photoinitiator is attached to the polymer.
The polymer is obtainable by free-radical addition polymerization from ethylenically unsaturated free-radically polymerizable compounds.
In the preferred case where the photoinitiator is attached to the polymer an ethylenically unsaturated compound having a photoinitiator group is preferably incorporated by copolymerization.